Indeed 4...Nc6 5.c3 Bf5 is one of the possibilities -- on a historical note, old theory cites a game Larsen-Spassky as equal. One quite recent product which addresses this stuff (albeit in German) is Elisabeth Pähtz's DVD on the London System, to wit:

I no longer play this line with either colour, but if I remember correctly, White's main idea is stopping Black's light-squared bishop from developing comfortably, so 4.Bd3 is the normal move rather than either 4.c3 or 4.Bf4. Presumably after 4.Bf4, Black can play 4...Nc6 5.c3 Bf5, or perhaps even 4...Bf5 immediately. Yes, you've stopped ...Qc7 if that's what you're concerned about, but allowing the bishop to come out to a good square arguably causes Black fewer development problems.

Is there any downside for White to use the move order 1.e4 c6 2.d4 d5 3. exd5 cxd5 4.Bf4 instead of the more usual 4.c3? 4.Bf4 stops lines with ...Qc7 in which Black prevents Bf4, so I was wondering if playing Bf4 right away is more accurate, or at least as good as 4.c3.